/*
 * Copyright 2011-2013 Blender Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifdef __OSL__
#  include "kernel/osl/osl_shader.h"
#endif

#include "kernel/kernel_random.h"
#include "kernel/kernel_projection.h"
#include "kernel/kernel_montecarlo.h"
#include "kernel/kernel_differential.h"
#include "kernel/kernel_camera.h"

#include "kernel/geom/geom.h"
#include "kernel/bvh/bvh.h"

#include "kernel/kernel_accumulate.h"
#include "kernel/kernel_shader.h"
#include "kernel/kernel_light.h"
#include "kernel/kernel_passes.h"

#ifdef __SUBSURFACE__
#  include "kernel/kernel_subsurface.h"
#endif

#ifdef __VOLUME__
#  include "kernel/kernel_volume.h"
#endif

#include "kernel/kernel_path_state.h"
#include "kernel/kernel_shadow.h"
#include "kernel/kernel_emission.h"
#include "kernel/kernel_path_common.h"
#include "kernel/kernel_path_surface.h"
#include "kernel/kernel_path_volume.h"
#include "kernel/kernel_path_subsurface.h"

CCL_NAMESPACE_BEGIN

ccl_device_forceinline bool kernel_path_scene_intersect(
	KernelGlobals *kg,
	ccl_addr_space PathState *state,
	Ray *ray,
	Intersection *isect,
	PathRadiance *L)
{
	uint visibility = path_state_ray_visibility(kg, state);

	if(path_state_ao_bounce(kg, state)) {
		visibility = PATH_RAY_SHADOW;
		ray->t = kernel_data.background.ao_distance;
	}

#ifdef __HAIR__
	float difl = 0.0f, extmax = 0.0f;
	uint lcg_state = 0;

	if(kernel_data.bvh.have_curves) {
		if((kernel_data.cam.resolution == 1) && (state->flag & PATH_RAY_CAMERA)) {
			float3 pixdiff = ray->dD.dx + ray->dD.dy;
			/*pixdiff = pixdiff - dot(pixdiff, ray.D)*ray.D;*/
			difl = kernel_data.curve.minimum_width * len(pixdiff) * 0.5f;
		}

		extmax = kernel_data.curve.maximum_width;
		lcg_state = lcg_state_init_addrspace(state, 0x51633e2d);
	}

	bool hit = scene_intersect(kg, *ray, visibility, isect, &lcg_state, difl, extmax);
#else
	bool hit = scene_intersect(kg, *ray, visibility, isect, NULL, 0.0f, 0.0f);
#endif  /* __HAIR__ */

#ifdef __KERNEL_DEBUG__
	if(state->flag & PATH_RAY_CAMERA) {
		L->debug_data.num_bvh_traversed_nodes += isect->num_traversed_nodes;
		L->debug_data.num_bvh_traversed_instances += isect->num_traversed_instances;
		L->debug_data.num_bvh_intersections += isect->num_intersections;
	}
	L->debug_data.num_ray_bounces++;
#endif  /* __KERNEL_DEBUG__ */

	return hit;
}

ccl_device_forceinline void kernel_path_lamp_emission(
	KernelGlobals *kg,
	ccl_addr_space PathState *state,
	Ray *ray,
	float3 throughput,
	ccl_addr_space Intersection *isect,
	ShaderData *emission_sd,
	PathRadiance *L)
{
#ifdef __LAMP_MIS__
	if(kernel_data.integrator.use_lamp_mis && !(state->flag & PATH_RAY_CAMERA)) {
		/* ray starting from previous non-transparent bounce */
		Ray light_ray;

		light_ray.P = ray->P - state->ray_t*ray->D;
		state->ray_t += isect->t;
		light_ray.D = ray->D;
		light_ray.t = state->ray_t;
		light_ray.time = ray->time;
		light_ray.dD = ray->dD;
		light_ray.dP = ray->dP;

		/* intersect with lamp */
		float3 emission;

		if(indirect_lamp_emission(kg, emission_sd, state, &light_ray, &emission))
			path_radiance_accum_emission(L, state, throughput, emission);
	}
#endif  /* __LAMP_MIS__ */
}

ccl_device_forceinline void kernel_path_background(
	KernelGlobals *kg,
	ccl_addr_space PathState *state,
	ccl_addr_space Ray *ray,
	float3 throughput,
	ShaderData *sd,
	PathRadiance *L)
{
	/* eval background shader if nothing hit */
	if(kernel_data.background.transparent && (state->flag & PATH_RAY_CAMERA)) {
		L->transparent += average(throughput);

#ifdef __PASSES__
		if(!(kernel_data.film.light_pass_flag & PASSMASK(BACKGROUND)))
#endif  /* __PASSES__ */
			return;
	}

	/* When using the ao bounces approximation, adjust background
	 * shader intensity with ao factor. */
	if(path_state_ao_bounce(kg, state)) {
		throughput *= kernel_data.background.ao_bounces_factor;
	}

#ifdef __BACKGROUND__
	/* sample background shader */
	float3 L_background = indirect_background(kg, sd, state, ray);
	path_radiance_accum_background(L, state, throughput, L_background);
#endif  /* __BACKGROUND__ */
}

#ifndef __SPLIT_KERNEL__

#ifdef __VOLUME__
ccl_device_forceinline VolumeIntegrateResult kernel_path_volume(
	KernelGlobals *kg,
	ShaderData *sd,
	PathState *state,
	Ray *ray,
	float3 *throughput,
	ccl_addr_space Intersection *isect,
	bool hit,
	ShaderData *emission_sd,
	PathRadiance *L)
{
	/* Sanitize volume stack. */
	if(!hit) {
		kernel_volume_clean_stack(kg, state->volume_stack);
	}

	if(state->volume_stack[0].shader == SHADER_NONE) {
		return VOLUME_PATH_ATTENUATED;
	}

	/* volume attenuation, emission, scatter */
	Ray volume_ray = *ray;
	volume_ray.t = (hit)? isect->t: FLT_MAX;

	bool heterogeneous = volume_stack_is_heterogeneous(kg, state->volume_stack);

#  ifdef __VOLUME_DECOUPLED__
	int sampling_method = volume_stack_sampling_method(kg, state->volume_stack);
	bool direct = (state->flag & PATH_RAY_CAMERA) != 0;
	bool decoupled = kernel_volume_use_decoupled(kg, heterogeneous, direct, sampling_method);

	if(decoupled) {
		/* cache steps along volume for repeated sampling */
		VolumeSegment volume_segment;

		shader_setup_from_volume(kg, sd, &volume_ray);
		kernel_volume_decoupled_record(kg, state,
			&volume_ray, sd, &volume_segment, heterogeneous);

		volume_segment.sampling_method = sampling_method;

		/* emission */
		if(volume_segment.closure_flag & SD_EMISSION)
			path_radiance_accum_emission(L, state, *throughput, volume_segment.accum_emission);

		/* scattering */
		VolumeIntegrateResult result = VOLUME_PATH_ATTENUATED;

		if(volume_segment.closure_flag & SD_SCATTER) {
			int all = kernel_data.integrator.sample_all_lights_indirect;

			/* direct light sampling */
			kernel_branched_path_volume_connect_light(kg, sd,
				emission_sd, *throughput, state, L, all,
				&volume_ray, &volume_segment);

			/* indirect sample. if we use distance sampling and take just
			 * one sample for direct and indirect light, we could share
			 * this computation, but makes code a bit complex */
			float rphase = path_state_rng_1D(kg, state, PRNG_PHASE_CHANNEL);
			float rscatter = path_state_rng_1D(kg, state, PRNG_SCATTER_DISTANCE);

			result = kernel_volume_decoupled_scatter(kg,
				state, &volume_ray, sd, throughput,
				rphase, rscatter, &volume_segment, NULL, true);
		}

		/* free cached steps */
		kernel_volume_decoupled_free(kg, &volume_segment);

		if(result == VOLUME_PATH_SCATTERED) {
			if(kernel_path_volume_bounce(kg, sd, throughput, state, &L->state, ray))
				return VOLUME_PATH_SCATTERED;
			else
				return VOLUME_PATH_MISSED;
		}
		else {
			*throughput *= volume_segment.accum_transmittance;
		}
	}
	else
#  endif  /* __VOLUME_DECOUPLED__ */
	{
		/* integrate along volume segment with distance sampling */
		VolumeIntegrateResult result = kernel_volume_integrate(
			kg, state, sd, &volume_ray, L, throughput, heterogeneous);

#  ifdef __VOLUME_SCATTER__
		if(result == VOLUME_PATH_SCATTERED) {
			/* direct lighting */
			kernel_path_volume_connect_light(kg, sd, emission_sd, *throughput, state, L);

			/* indirect light bounce */
			if(kernel_path_volume_bounce(kg, sd, throughput, state, &L->state, ray))
				return VOLUME_PATH_SCATTERED;
			else
				return VOLUME_PATH_MISSED;
		}
#  endif  /* __VOLUME_SCATTER__ */
	}

	return VOLUME_PATH_ATTENUATED;
}
#endif  /* __VOLUME__ */

#endif /* __SPLIT_KERNEL__ */

ccl_device_forceinline bool kernel_path_shader_apply(
	KernelGlobals *kg,
	ShaderData *sd,
	ccl_addr_space PathState *state,
	ccl_addr_space Ray *ray,
	float3 throughput,
	ShaderData *emission_sd,
	PathRadiance *L,
	ccl_global float *buffer)
{
#ifdef __SHADOW_TRICKS__
	if((sd->object_flag & SD_OBJECT_SHADOW_CATCHER)) {
		if(state->flag & PATH_RAY_CAMERA) {
			state->flag |= (PATH_RAY_SHADOW_CATCHER |
						   PATH_RAY_STORE_SHADOW_INFO);

			float3 bg = make_float3(0.0f, 0.0f, 0.0f);
			if(!kernel_data.background.transparent) {
				bg = indirect_background(kg, emission_sd, state, ray);
			}
			path_radiance_accum_shadowcatcher(L, throughput, bg);
		}
	}
	else if(state->flag & PATH_RAY_SHADOW_CATCHER) {
		/* Only update transparency after shadow catcher bounce. */
		L->shadow_transparency *=
				average(shader_bsdf_transparency(kg, sd));
	}
#endif  /* __SHADOW_TRICKS__ */

	/* holdout */
#ifdef __HOLDOUT__
	if(((sd->flag & SD_HOLDOUT) ||
		(sd->object_flag & SD_OBJECT_HOLDOUT_MASK)) &&
	   (state->flag & PATH_RAY_CAMERA))
	{
		if(kernel_data.background.transparent) {
			float3 holdout_weight;
			if(sd->object_flag & SD_OBJECT_HOLDOUT_MASK) {
				holdout_weight = make_float3(1.0f, 1.0f, 1.0f);
			}
			else {
				holdout_weight = shader_holdout_eval(kg, sd);
			}
			/* any throughput is ok, should all be identical here */
			L->transparent += average(holdout_weight*throughput);
		}

		if(sd->object_flag & SD_OBJECT_HOLDOUT_MASK) {
			return false;
		}
	}
#endif  /* __HOLDOUT__ */

	/* holdout mask objects do not write data passes */
	kernel_write_data_passes(kg, buffer, L, sd, state, throughput);

	/* blurring of bsdf after bounces, for rays that have a small likelihood
	 * of following this particular path (diffuse, rough glossy) */
	if(kernel_data.integrator.filter_glossy != FLT_MAX) {
		float blur_pdf = kernel_data.integrator.filter_glossy*state->min_ray_pdf;

		if(blur_pdf < 1.0f) {
			float blur_roughness = sqrtf(1.0f - blur_pdf)*0.5f;
			shader_bsdf_blur(kg, sd, blur_roughness);
		}
	}

#ifdef __EMISSION__
	/* emission */
	if(sd->flag & SD_EMISSION) {
		float3 emission = indirect_primitive_emission(kg, sd, sd->ray_length, state->flag, state->ray_pdf);
		path_radiance_accum_emission(L, state, throughput, emission);
	}
#endif  /* __EMISSION__ */

	return true;
}

ccl_device_noinline void kernel_path_ao(KernelGlobals *kg,
                                        ShaderData *sd,
                                        ShaderData *emission_sd,
                                        PathRadiance *L,
                                        ccl_addr_space PathState *state,
                                        float3 throughput,
                                        float3 ao_alpha)
{
	/* todo: solve correlation */
	float bsdf_u, bsdf_v;

	path_state_rng_2D(kg, state, PRNG_BSDF_U, &bsdf_u, &bsdf_v);

	float ao_factor = kernel_data.background.ao_factor;
	float3 ao_N;
	float3 ao_bsdf = shader_bsdf_ao(kg, sd, ao_factor, &ao_N);
	float3 ao_D;
	float ao_pdf;

	sample_cos_hemisphere(ao_N, bsdf_u, bsdf_v, &ao_D, &ao_pdf);

	if(dot(sd->Ng, ao_D) > 0.0f && ao_pdf != 0.0f) {
		Ray light_ray;
		float3 ao_shadow;

		light_ray.P = ray_offset(sd->P, sd->Ng);
		light_ray.D = ao_D;
		light_ray.t = kernel_data.background.ao_distance;
		light_ray.time = sd->time;
		light_ray.dP = sd->dP;
		light_ray.dD = differential3_zero();

		if(!shadow_blocked(kg, sd, emission_sd, state, &light_ray, &ao_shadow)) {
			path_radiance_accum_ao(L, state, throughput, ao_alpha, ao_bsdf, ao_shadow);
		}
		else {
			path_radiance_accum_total_ao(L, state, throughput, ao_bsdf);
		}
	}
}

#ifndef __SPLIT_KERNEL__

#if defined(__BRANCHED_PATH__) || defined(__BAKING__)

ccl_device void kernel_path_indirect(KernelGlobals *kg,
                                     ShaderData *sd,
                                     ShaderData *emission_sd,
                                     Ray *ray,
                                     float3 throughput,
                                     PathState *state,
                                     PathRadiance *L)
{
	/* path iteration */
	for(;;) {
		/* Find intersection with objects in scene. */
		Intersection isect;
		bool hit = kernel_path_scene_intersect(kg, state, ray, &isect, L);

		/* Find intersection with lamps and compute emission for MIS. */
		kernel_path_lamp_emission(kg, state, ray, throughput, &isect, sd, L);

#ifdef __VOLUME__
		/* Volume integration. */
		VolumeIntegrateResult result = kernel_path_volume(kg,
		                                                   sd,
		                                                   state,
		                                                   ray,
		                                                   &throughput,
		                                                   &isect,
		                                                   hit,
		                                                   emission_sd,
		                                                   L);

		if(result == VOLUME_PATH_SCATTERED) {
			continue;
		}
		else if(result == VOLUME_PATH_MISSED) {
			break;
		}
#endif /* __VOLUME__*/

		/* Shade background. */
		if(!hit) {
			kernel_path_background(kg, state, ray, throughput, sd, L);
			break;
		}
		else if(path_state_ao_bounce(kg, state)) {
			break;
		}

		/* Setup and evaluate shader. */
		shader_setup_from_ray(kg,
		                      sd,
		                      &isect,
		                      ray);
		shader_eval_surface(kg, sd, state, state->flag, kernel_data.integrator.max_closures);
		shader_prepare_closures(sd, state);

		/* Apply shadow catcher, holdout, emission. */
		if(!kernel_path_shader_apply(kg,
		                             sd,
		                             state,
		                             ray,
		                             throughput,
		                             emission_sd,
		                             L,
		                             NULL))
		{
			break;
		}

		/* path termination. this is a strange place to put the termination, it's
		 * mainly due to the mixed in MIS that we use. gives too many unneeded
		 * shader evaluations, only need emission if we are going to terminate */
		float probability = path_state_continuation_probability(kg, state, throughput);

		if(probability == 0.0f) {
			break;
		}
		else if(probability != 1.0f) {
			float terminate = path_state_rng_1D(kg, state, PRNG_TERMINATE);

			if(terminate >= probability)
				break;

			throughput /= probability;
		}

		kernel_update_denoising_features(kg, sd, state, L);

#ifdef __AO__
		/* ambient occlusion */
		if(kernel_data.integrator.use_ambient_occlusion || (sd->flag & SD_AO)) {
			kernel_path_ao(kg, sd, emission_sd, L, state, throughput, make_float3(0.0f, 0.0f, 0.0f));
		}
#endif  /* __AO__ */

#ifdef __SUBSURFACE__
		/* bssrdf scatter to a different location on the same object, replacing
		 * the closures with a diffuse BSDF */
		if(sd->flag & SD_BSSRDF) {
			float bssrdf_u, bssrdf_v;
			path_state_rng_2D(kg,
			                  state,
			                  PRNG_BSDF_U,
			                  &bssrdf_u, &bssrdf_v);

			const ShaderClosure *sc = shader_bssrdf_pick(sd, &throughput, &bssrdf_u);

			/* do bssrdf scatter step if we picked a bssrdf closure */
			if(sc) {
				uint lcg_state = lcg_state_init(state, 0x68bc21eb);

				subsurface_scatter_step(kg,
				                        sd,
				                        state,
				                        state->flag,
				                        sc,
				                        &lcg_state,
				                        bssrdf_u, bssrdf_v,
				                        false);
			}
		}
#endif  /* __SUBSURFACE__ */

#if defined(__EMISSION__)
		if(kernel_data.integrator.use_direct_light) {
			int all = (kernel_data.integrator.sample_all_lights_indirect) ||
			          (state->flag & PATH_RAY_SHADOW_CATCHER);
			kernel_branched_path_surface_connect_light(kg,
			                                           sd,
			                                           emission_sd,
			                                           state,
			                                           throughput,
			                                           1.0f,
			                                           L,
			                                           all);
		}
#endif  /* defined(__EMISSION__) */

		if(!kernel_path_surface_bounce(kg, sd, &throughput, state, &L->state, ray))
			break;
	}
}

#endif /* defined(__BRANCHED_PATH__) || defined(__BAKING__) */

ccl_device_forceinline void kernel_path_integrate(
	KernelGlobals *kg,
	PathState *state,
	float3 throughput,
	Ray *ray,
	PathRadiance *L,
	ccl_global float *buffer,
	ShaderData *emission_sd)
{
	/* Shader data memory used for both volumes and surfaces, saves stack space. */
	ShaderData sd;

#ifdef __SUBSURFACE__
	SubsurfaceIndirectRays ss_indirect;
	kernel_path_subsurface_init_indirect(&ss_indirect);

	for(;;) {
#endif  /* __SUBSURFACE__ */

	/* path iteration */
	for(;;) {
		/* Find intersection with objects in scene. */
		Intersection isect;
		bool hit = kernel_path_scene_intersect(kg, state, ray, &isect, L);

		/* Find intersection with lamps and compute emission for MIS. */
		kernel_path_lamp_emission(kg, state, ray, throughput, &isect, &sd, L);

#ifdef __VOLUME__
		/* Volume integration. */
		VolumeIntegrateResult result = kernel_path_volume(kg,
		                                                   &sd,
		                                                   state,
		                                                   ray,
		                                                   &throughput,
		                                                   &isect,
		                                                   hit,
		                                                   emission_sd,
		                                                   L);

		if(result == VOLUME_PATH_SCATTERED) {
			continue;
		}
		else if(result == VOLUME_PATH_MISSED) {
			break;
		}
#endif /* __VOLUME__*/

		/* Shade background. */
		if(!hit) {
			kernel_path_background(kg, state, ray, throughput, &sd, L);
			break;
		}
		else if(path_state_ao_bounce(kg, state)) {
			break;
		}

		/* Setup and evaluate shader. */
		shader_setup_from_ray(kg, &sd, &isect, ray);
		shader_eval_surface(kg, &sd, state, state->flag, kernel_data.integrator.max_closures);
		shader_prepare_closures(&sd, state);

		/* Apply shadow catcher, holdout, emission. */
		if(!kernel_path_shader_apply(kg,
		                             &sd,
		                             state,
		                             ray,
		                             throughput,
		                             emission_sd,
		                             L,
		                             buffer))
		{
			break;
		}

		/* path termination. this is a strange place to put the termination, it's
		 * mainly due to the mixed in MIS that we use. gives too many unneeded
		 * shader evaluations, only need emission if we are going to terminate */
		float probability = path_state_continuation_probability(kg, state, throughput);

		if(probability == 0.0f) {
			break;
		}
		else if(probability != 1.0f) {
			float terminate = path_state_rng_1D(kg, state, PRNG_TERMINATE);
			if(terminate >= probability)
				break;

			throughput /= probability;
		}

		kernel_update_denoising_features(kg, &sd, state, L);

#ifdef __AO__
		/* ambient occlusion */
		if(kernel_data.integrator.use_ambient_occlusion || (sd.flag & SD_AO)) {
			kernel_path_ao(kg, &sd, emission_sd, L, state, throughput, shader_bsdf_alpha(kg, &sd));
		}
#endif  /* __AO__ */

#ifdef __SUBSURFACE__
		/* bssrdf scatter to a different location on the same object, replacing
		 * the closures with a diffuse BSDF */
		if(sd.flag & SD_BSSRDF) {
			if(kernel_path_subsurface_scatter(kg,
			                                  &sd,
			                                  emission_sd,
			                                  L,
			                                  state,
			                                  ray,
			                                  &throughput,
			                                  &ss_indirect))
			{
				break;
			}
		}
#endif  /* __SUBSURFACE__ */

		/* direct lighting */
		kernel_path_surface_connect_light(kg, &sd, emission_sd, throughput, state, L);

		/* compute direct lighting and next bounce */
		if(!kernel_path_surface_bounce(kg, &sd, &throughput, state, &L->state, ray))
			break;
	}

#ifdef __SUBSURFACE__
		/* Trace indirect subsurface rays by restarting the loop. this uses less
		 * stack memory than invoking kernel_path_indirect.
		 */
		if(ss_indirect.num_rays) {
			kernel_path_subsurface_setup_indirect(kg,
			                                      &ss_indirect,
			                                      state,
			                                      ray,
			                                      L,
			                                      &throughput);
		}
		else {
			break;
		}
	}
#endif  /* __SUBSURFACE__ */
}

ccl_device void kernel_path_trace(KernelGlobals *kg,
	ccl_global float *buffer,
	int sample, int x, int y, int offset, int stride)
{
	/* buffer offset */
	int index = offset + x + y*stride;
	int pass_stride = kernel_data.film.pass_stride;

	buffer += index*pass_stride;

	/* Initialize random numbers and sample ray. */
	uint rng_hash;
	Ray ray;

	kernel_path_trace_setup(kg, sample, x, y, &rng_hash, &ray);

	if(ray.t == 0.0f) {
		return;
	}

	/* Initialize state. */
	float3 throughput = make_float3(1.0f, 1.0f, 1.0f);

	PathRadiance L;
	path_radiance_init(&L, kernel_data.film.use_light_pass);

	ShaderDataTinyStorage emission_sd_storage;
	ShaderData *emission_sd = AS_SHADER_DATA(&emission_sd_storage);

	PathState state;
	path_state_init(kg, emission_sd, &state, rng_hash, sample, &ray);

	/* Integrate. */
	kernel_path_integrate(kg,
	                      &state,
	                      throughput,
	                      &ray,
	                      &L,
	                      buffer,
	                      emission_sd);

	kernel_write_result(kg, buffer, sample, &L);
}

#endif  /* __SPLIT_KERNEL__ */

CCL_NAMESPACE_END

